Evaporation system

ABSTRACT

A system for preserving perishable goods in an enclosed transport container including an insulated evaporator for liquefied gas arranged to produce a layer of cold dense gas to envelop the goods and to maintain them at a temperature below ambient.

United States, Patent 1191 11] 3,79,6fl6 Davidge Feb. 5, 1974 [5 EVAPORATION SYSTEM 2,479,866 8/1949 Rosebaugh 62/45 x 2,496,816 2/1950 Schlumbohm 62/514 X [75] lnvemor- Hamid London England 3,316,726 5/1967 Pauliukonis 62/55 [73] Assignee: The British Oxygen Company g i et 7 Y ec man London England 3,304,728 2/1967 De Haan 62/45 [22] Filed: June 23, 1971 3,611,738 10 1971 Maurer et al. 62/514 x 3,491,910 l/1970 Buckwalter et al. 220/9 LG [21] Appl. No: 156,018

Primary ExaminerMeyer Perlin [30] Foreign Application Priority Data Assistant Examiner-Ronald C. Capossela June 24, 1970 Great Britain 30577/70 Attorney, g or Firm-Robert I. Dennison er Apr. 16, 1971 Great Britain 9586/71 57 ABSTRACT 52 us. (:1. 62/511, 62/514 1 [51] Int. Cl. Fl7c 7/04 A System for Preservmg perishable goods In an 58 Field of Search 62/45, 50, 51, 514 closed transport container including an insulated evaporator for liquefied gas arranged to produce a [56] References Cited layer of cold dense gas to envelop the goods and to UNITED STATES PATENTS maintain them at a temperature below ambient. 677,837 7 1901 W rightnour 62/514 x 21 Claims, 3 Drawing Figures PATENIE FEB 5:974

SHEET 2 0F 3 FIGQ2' l EVAPORATION SYSTEM FIELD OF THE INVENTION This invention relates to the provision of an evaporation system in a container for perishable goods so as to DESCRIPTION OF THE PRIOR ART Previous proposals have been made for cooling an insulated food container by the provision of a source of liquefied gas connected to a thermostatically controlled valved spray system so as to deliver nitrogen to the container and thus to maintain a temperature at which deterioration of the food is reduced. Such systems have been relatively complex and the low temperatures at which they have been required to operate have given rise to problems in controlling the operation of the thermostat and of the valves. The invention relates to a simplified form of cold gas delivery system having the advantage of requiring no moving parts.

SUMMARY OF THE INVENTION According to the invention there is provided apparatus for supplying evaporated gas to an enclosed space including a liquefied gas evaporator having a shell constructed of gas-impermeable material, a layer of insulating material, an inlet for liquefied gas and a vapour outlet leading directly to the enclosed space, wherein the location and dimensions of the vapour outlet permit the escape of dense, non-turbulent evaporated gas.

Preferably the mean thermal conductivity of the evaporator is within the range 0.08 to 0.155 BTU/ sq ft/inch/F/hour.

The invention also relates to a method of preserving perishable goods such as foodstuffs by using such an evaporator in an enclosed transport container holding the goods.

The evaporator provides a source of cold gas in an enclosed transport container that provides cooling in the container and also envelopes the contents of the container in a layer of dense evaporated'gas. This layer is extremely effective in maintaining at low temperature cold packages such as frozen food cartons. The layer is produced because of the evaporation of the liquefied gas into a region of low turbulence. It is thus important to avoid turbulent conditions, such as would be produced by the intermittent spraying of liquefied gas or by the use of solid carbon dioxide as coolant in the container. Formation of the dense layer is also assisted by locating the evaporator outlet at a high level in the container. If the evaporator itself is located at a low level it is preferably provided with a chimney to convey the dense gas to a high level in the container.

l have found that the packaging effect of the dense vapour is such that the temperature of the packages is maintained at a substantially constant level. Surprisingly this effect applies both to frozen food (for example at about l8C) and to chilled food (for example at about +4C). Indeed my trials have shown that the ability of the layer of dense vapour to maintain packages at a reduced temperature is much greater than the heat extraction effect of the liquefied gas. The most im portant requirement of the container is that it should promote non-turbulent conditions Indeed the insulation of the material of the container can be very small indeed and accordingly it is possible to use a standard transport container having no special insulation.

The evaporator must of course be of a size that can produce the desired volume of dense gas for a given period. With road transport vehicles the period for which gas production is required will normally be within the range 8-12 hours. Preferably a volume of liquefied gas within the range 0.5 to 2.0 kg/hour is evaporated for each cubic metre of the container.

The liquefied gas is preferably liquid nitrogen or liquid argon.

The evaporator shell can be constructed from metal or a plastics material. Examples of particularly suitable materials are aluminium, stainless steel and polytetrafluorethylene. If desired the shell can be a composite structure of alternate layers of metal and plastics material.

The insulating layer is preferably formed from a solid insulant, for example a foamed plastics material such as foamed polystyrene, and can be in the form of powdered or granular material or of continuous layers or slabs. It is preferably enclosed within an outer shell which, like the inner shell, can be constructed of metal or a plastics material. One particularly suitable solid insulant is a strip of foamed polystyrene wrapped around the inner shell. This allows simple manufacture of the evaporator.

If no outer skin is provided, or only a partial skin, the insulation is desirably so disposed about the shell that there is no exposed part of the shell at a temperature low enough to present a hazard if touched.

The insulating layer can alternatively be provided by a gas such as air or nitrogen in which case an outer shell must be provided to keep the insulating layer in position.

A drip tray is preferably provided at the base of the evaporator and desirably is fitted with a drainage tube to communicate with the exterior of the container.

The interior of the evaporator is preferable fitted with support members. These are helpful in allowing the evaporator to withstand the strains resulting from filling the evaporator at a temperature above 0C with liquefied gas at a temperature of the order of --200C. They also act to damp the movement of liquid in the evaporator while in motion. The preferred form of support is a perforated baffle plate laterally disposed in the evaporator. At least two such supports are generally desirable.

It has been found that an evaporator of elongated shape mounted with its longest dimension vertical is generally preferred. With such an evaporator the dense evaporated gas flowing downwards over the external surface forms an insulating jacket for the evaporator and thus allows the amount of insulant built into the evaporator to be kept to a minimumrSuch an evaporator is preferably of oval horizontal cross section. This allows the evaporator to protrude less into the load carrying space of the container than would a circular cross section and provide a stronger construction than would a square or rectangular cross section.

The vapour outlet is preferably circular and preferably centrally disposed in the upper surface of the evaporator. It is preferably not so small-that it is likely to be blocked by ice formation or to cause a turbulent gas stream. For a circular outlet this'is likely to occur if a diameter of less than 25mm is employed. It will follow that for any shaped outlet the cross-sectional area thereof must not be smaller than approximately 491 square mm. Similarly the vapour outlet should not be so large as to permit large volumes of warm gas to enter and come into contact with the liquefied gas. Thus the area of outlet relative to the area of the upper surface of liquid in the evaporator is preferably within the range 1:8 to 1:80.

Although several outlets can be provided for the evaporated gas it is preferred to employ a single outlet. This helps to give a non-turbulent flow of evaporated gas from the evaporator.

Although the vapour outlet can serve as the liquid inlet, it is generally preferable to provide a liquid inlet separate from the vapour outlet. The evaporator can either be filled when in situ in the container or, if portable, can be filled outside the container and then placed in the desired position in the container. In one convenient form the container is provided with a supply pipe leading from an evaporator inside the container to a supply port outside the container, thus enabling the evaporator to be filled from outside the container.

Any exposed pipes leading to the evaporator should desirably be enclosed in a protective layer. This reduces cold losses from the evaporator and also provides protection against cold burns for anyone who enters the container.

If the evaporator has an inner shell and an outer shell, the upper inner surface of the inner shell is preferably perforated. This ensures that evaporated gas can enter the space between the two shells and thus reduces the possibility that air could be condensed in this space to give liquid air of enriched oxygen content. Such enriched air can prove dangerous if it comes into contact with inflammable material in the space.

The container in which the evaporator is located is preferably provided both with a written warning that gases such as nitrogen and argon, while not poisonous, can cause asphyxiation and a written warning that care should be taken when filling the evaporator to prevent build up of pressure in the container.

The invention will now be described with reference to the accompanying drawings, in which;

FIG. 1 is a sectional elevation of one form of evaporator mounted in an insulated container.

FIG. 2 is a sectional elevation along the line AA of the evaporator shown in FIG. 1.

FIG. 3 is a sectional elevation of a second form of evaporator mounted in an insulated container.

The evaporator shown in FIGS. 1 and 2 comprises an inner shell 2 constructed of stainless steel enclosed in a shell 4 made up of layers of foamed polystyrene and covered with a coating layer 6 of polypropylene.

An inlet 8 leads into the inner shell 2 and connects with an inlet pipe 10 leading from outside an insulated container 12. The inlet pipe 10 has a valved inlet 14 located outside the container 12. An overflow 16 leads from the upper part of the interior of the shell 2 through a conduit 18 to outside the container 12.

In the top surface of the shell 2 a cylindrical outlet 20 is provided passing through the shell 2 of insulating material and coating layer 6.

The thermal conductivity of the evaporator is preferably 0.1 l BTU/sq ft/inch/F/hour.

The external dimensions of the preferred evaporator are 1.6 meters wide X 0.4 meters high X 0.3 meters 4 deep. The inlet pipe 10 is a 25 mm diameter tube and the outlet 20 is a 35mm diameter cylinder.

In operation liquefied gas is introduced into the shell 22 until the liquid level reaches the inlet of overflow 16. Dense vapour then escapes through the outlet 20 into the container 12.

The evaporator shown in FIG. 3 has an inner shell 2 of aluminium and of oval cross section covered by an insulating layer 4 made by wrapping first cloth and then polystyrene strip on the inner shell 2. The insulating layer is enclosed within an outer shell 5 of aluminium. The outer shell 5 stands in a drip tray 9 mounted on the floor 10 of the container adjacent to the container wall 12. A circular opening 15 is provided in the center of the upper end of the shells 2 and 5 and insulating layer 4. The upper surface of the inner shell 2 has perforations as indicated by the numeral 17. Perforated baffle plates 19 are provided inside the inner shell 2. A filler pipe 21 and overflow pipe 22 lead from a hollow boss 24 on the outside of the container wall 12 to the upper part of the inside of the inner shell 2. The filler pipe 21 passes straight through the boss 24 and is closed by a filler cap 26 fitted with a washer 28. The overflow pipe 22 leads to the inside of the hollow boss 24 and communicates with an overflow port 30.

Insulation 32 is provided around the exposed portions of pipes 21 and 22 and a drain pipe 34 is provided in the base of the drip tray 9, leading through the wall 12 to the outside of the container.

To fill the evaporator the filler cap 26 is removed and liquefied gas from a reservoir is fed into the evaporator. If the evaporator is initially at ambient temperature the liquefied gas initially introduced will evaporate rapidly, providing cold evaporated gas to cool the evaporator and the interior of the container. When the level of liquefied gas reaches the top of the overflow pipe 22 liquefied gas flows through the pipe 22, boss 24 and port 30, indicating that the evaporator is full.

The evaporator described above is 1. ng rs l 1 ig h ofa maximum diameter of0.30 meters and the opening 15 has a diameter of 75mm. It has a mean thermal conductivity of 0.1 1 BTU/sq ft/inch/F /hour at the temperature of evaporating liquid nitrogen (196C).

1 claim:

1. In combination with an enclosed cold storage container, an unpressurized liquefied cryogenic gas evaporator for supplying evaporated gas to said container, said evaporator having a shell formed of gasimpermeable material, a layer of insulating material on the outside of said shell, an inlet into said evaporator for the introducing of liquefied gas, and unconstricted vapour outlet means in the top of said evaporator, said vapour outlet means having a minimum area of 491 square mm, a maximum area equal to one-eighth of the upper surface area of the liquid in the evaporator, and

4. A container as claimed in claim 1, wherein the evaporator is located at a low level with respect to the floor of the container and is provided with a chimney to convey the dense gas to a relatively high level with respect to said floor.

5. A container as claimed in claim 1, wherein the evaporator shell is constructed from metal.

6. A container as claimed in claim 1, wherein the evaporator shell is constructed from a plastic material.

7. A container as claimed in claim 1, wherein the evaporator shell is a composite structure of alternate layers of metal and plastic materials.

8. A container as claimed in claim 1, wherein the vapour outlet means is centrally disposed in the upper surface of the evaporator.

9. A container as claimed in claim 1, wherein the evaporator has an inner shell and an outer shell and the upper inner surface of the inner shell is perforated.

10. A container as claimed in claim 1, wherein the insulating layer of the evaporator is enclosed within an outer shell.

11. A container as claimed in claim 10, wherein the insulating layer is provided by a gas.

12. A container as claimed in claim 1, wherein the insulating layer of the evaporator is formed from a solid insulant.

13. A container as claimed in claim 12, wherein the solid insulant is a foamed plastic material.

14. A container as claimed in claim 1, wherein the evaporator is provided with a drip tray.

15. A container as claimed in claim 14, wherein the drip tray has a drainage tube communicating with the exterior of the container.

16. A container as claimed in claim 1, wherein the interior of the evaporator is fitted with support members.

17. A container as claimed in claim 16, wherein the support members are perforated baffie plates laterally disposed in the evaporator.

18. A-container as claimed in claim 1, wherein the evaporator is of elongated shape with its longest dimension vertical.

19. A container as claimed in claim 18, wherein the evaporator is of oval horizontal cross-section.

20. A container as claimed in claim 1, and including a supply pipe leading from the inlet to a supply port outside the container.

21. A container as claimed in claim 20, wherein said pipe leading from the inlet is enclosed in a protective 

1. In combination with an enclosed cold storage container, an unpressurized liquefied cryogenic gas evaporator for supplying evaporated gas to said container, said evaporator having a shell formed of gas-impermeable material, a layer of insulating material on the outside of said shell, an inlet into said evaporator for the introducing of liquefied gas, and unconstricted vapour outlet means in the top of said evaporator, said vapour outlet means having a minimum area of 491 square mm, a maximum area equal to one-eighth of the upper surface area of the liquid in the evaporator, and leading directly to the enclosed container to permit the escape by direct evaporation of dense, nonturbulent evaporated cooling gas, said gas flowing out of said outlet means and over goods stored within said container to form an insulating blanket thereover.
 2. A container as claimed in claim 1, wherein the mean thermal conductivity of the evaporator is within the range 0.08 to 0.155 BTU/sq ft/inch/*F/hour.
 3. A container as claimed in claim 1, wherein the vapor outlet means is located at a high level with respect to the floor of the container.
 4. A container as claimed in claim 1, wherein the evaporator is located at a low level with respect to the floor of the container and is provided with a chimney to convey the dense gas to a relatively high level with respect to said floor.
 5. A container as claimed in claim 1, wherein the evaporator shell is constructed from metal.
 6. A container as claimed in claim 1, wherein the evaporator shell is constructed from a plastic material.
 7. A container as claimed in claim 1, wherein the evaporator shell is a composite structure of alternate layers of metal and plastic materials.
 8. A container as claimed in claim 1, wherein the vapour outlet means is centrally disposed in the upper surface of the evaporator.
 9. A container as claimed in claim 1, wherein the evaporator has an inner shell and an outer shell and the upper inner surface of the inner shell is perforated.
 10. A container as claimed in claim 1, wherein the insulating layer of the evaporator is enclosed within an outer shell.
 11. A container as claimed in claim 10, wherein the insulating layer is provided by a gas.
 12. A container as claimed in claim 1, wherein the insulating layer of the evaporator is formed from a solid insulant.
 13. A container as claimed in claim 12, wherein the soLid insulant is a foamed plastic material.
 14. A container as claimed in claim 1, wherein the evaporator is provided with a drip tray.
 15. A container as claimed in claim 14, wherein the drip tray has a drainage tube communicating with the exterior of the container.
 16. A container as claimed in claim 1, wherein the interior of the evaporator is fitted with support members.
 17. A container as claimed in claim 16, wherein the support members are perforated baffle plates laterally disposed in the evaporator.
 18. A container as claimed in claim 1, wherein the evaporator is of elongated shape with its longest dimension vertical.
 19. A container as claimed in claim 18, wherein the evaporator is of oval horizontal cross-section.
 20. A container as claimed in claim 1, and including a supply pipe leading from the inlet to a supply port outside the container.
 21. A container as claimed in claim 20, wherein said pipe leading from the inlet is enclosed in a protective layer. 